In order to assess the relative importance of intracellular pH changes as a determinant in cell division, we plan to measure intracellular pH over the cell cycle in synchronized populations of Euglena gracilis, using the DMO technique. The growth rate of Euglena in continuous light (asynchronous growth) is also modified by CO2 concentrations in predictable ways determined by the extracellular pH. We will determine intracellular pH under these various conditions to determine if there is a correlation between growth rate and intracellular pH.